You can report any "bug" you like.
How it's received depends a lot on how many other people are bothered by it, and how much they care.
So, for instance, if you report "If I click too quickly, Stack Overflow sets my house on fire" and 30 other people encounter the same problem, you'll probably find your report up-voted (and the bug fixed).
On the other hand, if you report "The shade of blue on Super User makes me sad" and no one else has ever encountered feelings of sadness upon viewing SU's glorious blue, you'll probably find your report either ignored completely, or down-voted for being a waste of time.
Pluralization bugs tend to fall somewhere in the middle. Generally, they don't bother very many people. Sometimes, they're clearly not even bugs. Almost always, the person reporting them hasn't really thought about how "fixing" them would make anyone's life better - they just see an "s" where, strictly-speaking, one doesn't need to exist, and post about it. YMMV...